(A) Purpose.
(1) This set of subdivision review regulations have been developed and approved by the Valencia Soil and Water Conservation District (herein referred to as the Valencia SWCD) at its regular meeting held on 3-20-2000.
(2) The purpose of these regulations is to set forth a minimum standard for review of subdivisions within the Valencia Soil and Water Conservation District in regard to terrain management.
(B) Definitions. For the purpose of this chapter, the following definitions shall apply unless the context clearly indicates or requires a different meaning.
COVER DENSITY. The estimated percentage of canopy and basal cover for each vegetative type; canopy cover being the estimated percentage of trees and shrubs that would shade the ground at midday and basal cover being the percentage of grasses, rocks, litter and desert pavement in direct contact with the ground.
DRAINAGE CHANNEL. Any depression into which stormwater flows along a defined course.
EROSION. Soil movement due to wind or water.
EROSION CONTROL STRUCTURE. Any manmade device for preventing or controlling erosion.
FLOOD FRINGE. Any area that will be flooded by water from a 50 year frequency storm.
FLOODPLAIN. Any area, which will be flooded by water from a 100 year frequency storm.
FLOODWAY. Any area that will be flooded by water from a 25-year frequency storm.
LOCAL DISTRICT. Any soil and water conservation district within the county in which the proposed subdivision is located.
SEDIMENT. Any soil or other surface material transported by wind or surface water as a product of erosion.
SOIL SURVEY. A soil survey conducted to USDA, Natural Resources Conservation Service national cooperative soil survey standards, or any other survey containing information of comparable quality and detail following the national standards for an Order 2 survey approved by the local district.
TERRAIN MANAGEMENT. The control of stormwaters, drainage, erosion and measures required for adapting proposed development to existing soil characteristics and topography.
WATERCOURSE. Any river, creek, spring, stream, arroyo, or any other like body having definable banks and/or evidencing the overland flow of water.
(C) Determination. The Soil and Water Conservation District shall determine as directed by state statute:
(1) Whether the subdivider can furnish terrain management sufficient to protect against flooding, inadequate drainage and erosion; and the proper utilization and disposal of water; and
(2) Whether the subdivider can fulfill the proposals contained in their disclosure statement concerning terrain management.
(D) Plan. A terrain management plan shall include:
(1) Vicinity map. A map drawn to a scale of not more than 200 feet to 1 inch showing the relationship of the site to its general surroundings, and the location of all existing drainage channels, water courses, and water bodies within 3 miles of the site. This map shall display the topographic contours at 20 feet intervals (a suitable example would be from a USGS Topographic Map).
(2) Natural features map. A map of the development (at the same scale as the plat map) showing directly or by overlay:
(a) The boundaries of the development;
(b) The existing contours with intervals of not less than 2 feet where the slope is less than 8% and not more than 5 feet where the slope is 8% or greater;
(c) All areas with natural slopes of 25% or greater clearly recorded by scale, line or color;
(d) The location of all drainage channels, watercourses, water bodies, floodways, flood fringes and floodplains; and
(e) The location of all major rock outcropping, faults and geologic resources.
(3) Soil survey. A soil survey of the site including:
(a) An overlay of the natural features map showing the location of each soil type. Soil surveys will be in keeping with the national standards as set forth by the USDA Natural Resources Conservation Service, (herein after referred to as the NRCS); and
(b) A description of the soil types. Detailed soil descriptions are required by the Valencia SWCD. Interpretations of the limitations from a detailed soil survey for each soil type for the intended land uses common to the development, and the proposed mitigation for each of the intended land uses proposed for the development.
(4) Grading plan.
(a) A series of maps, cross sections, and design profiles showing the location and impact of the planned development features to the natural land form;
(b) An overlay of the natural features map showing the location of all proposed parcels, roads, bridges, water and erosion control structures, and the utility easements in relation to the existing contours;
(c) An overlay showing the finished contours of the development after all proposals have been implemented using contour intervals equal to or less than those on the existing contour map;
(d) The location of all cuts and fills, including the grades, lengths and depths thereof,
displayed using the necessary cross section and profiles to adequately describe the planned action;
(e) The location of all areas where the natural elevation of the land will be changed by more than 3 feet;
(f) The location of all areas where the grading of land will disturb more than 5,000 contiguous square feet;
(g) Profiles showing the existing ground surface and proposed street grades and typical cross-sections of the proposed grading; and
(h) Description of methods of stabilization in areas of cut and fill, embankment compaction, and revegetation on steep slopes.
(5) Landscaping plan.
(a) A series of maps or overlays and narratives to identify those areas which will be revegetated following disturbance or the enhance the visual aesthetics of the site and the methods to be used;
(b) Location and type of materials to be used in revegetation and slope stabilization;
(c) Location of all areas where vegetation will be preserved and a description of the methods that will be used for protection;
(d) Duration of exposure of the disturbed sites before the reclamation of the site will take place;
(e) Description of the methods to be used to minimize erosion of the disturbed sites prior to reclamation description of the vegetative characteristics that will be present after revegetation; and
(f) The plan for site preparation, fertilization, seeding rates, dates and amounts by species, mulching type and amount for both grass, shrubs, and trees. If watering is a planned part of the revegetation procedure, a description of the planned irrigation system and amounts of water needed will be included.
(6) Erosion and drainage plan. This document shall include the necessary charts, drawings, location maps and calculations to support the plan:
(a) A watershed map showing all the upper watershed area draining into or through the site; it should show the water sources and topographic conditions as well as indicate the soil and vegetative types and their locations within the watershed;
(b) Storm drainage computations for the 100-year frequency storm both reaching and leaving the site in the pre-development conditions;
(c) Storm drainage calculations for the post development estimates of runoff after full development of the site; this shall state the estimated runoff before and after any mitigation of the increased flows;
(d) Quantities of water carried by the major watercourses and the proposed treatment of the watercourses;
(e) Calculations will be provided for pre- and post-development;
(f) The location, type and size of all proposed drainage and erosion control structures with adequate detail of the drawings or designs;
(g) The location and size of drainage easements will be shown on the plat map for all floodplains, floodways, flood fringes, and other natural water courses, along with adequate supporting documentation;
(h) Drainage easements are required for all watercourses with 100-year storm flows that exceed 20 cubic feet per second flow rates;
(I) An overlay indicating the depth to ground water in all areas where the seasonal high water table is within 20 feet of the ground surface; and
(j) All appropriate design details necessary to clearly explain the construction of all surface and subsurface structures.
(7) Floodplain management plan. Subdivisions and developments shall be planned, constructed, and maintained so that structures, material deposits or excavations, alone or in combination with present future works, do not adversely affect the capacity of the floodplain.
(E) Materials included. The flood hazard analysis will include all needed maps, inventories and calculations to provide for adequate documentation and review of the determinations made. The preferred method of watershed hydrology evaluation is NRCS Technical Release 55, "Urban Hydrology for Small Watersheds" or Chapter 2 of the NRCS Engineering Field Manual. Other methods such as the rational method are acceptable if sufficient. Supporting data is presented and deemed adequate by the reviewer. The use of FEMA flood hazard maps by itself is not adequate for locating all possible 100-year floodplains within the development.
(F) Construction schedule.
(1) The start and finish dates for all clearing, grubbing and grading activities.
(2) Duration of exposure of disturbed areas.
(3) Stabilization date for disturbed areas.
(4) Installation date of all storm drainage system components.
(5) Installation date for all roads and related structural measures.
(6) Paving dates for all roads or parking areas included in the site plan.
(7) Installation date of each utility to be provided and whether the utility will be above or below ground.
(8) Installation date for homes, recreation structures, and other community's facilities and improvements.
(G) Disclosure statement. Disclosure statement regarding terrain management shall include:
(1) Describe the suitability of the soils in the subdivision for residential use whether permanent or seasonal;
(2) Describe any measures necessary for overcoming soil topographic limitations, and who will be responsible for implementing these measures;
(3) Give the location of all lots with land areas within a floodway, flood fringe or floodplain;
(4) Give the location of all lots located on slopes in excess of 8%;
(5) Describe the subsurface drainage plan for all lots with water tables within 5 feet of the finished surface elevation;
(6) Describe the surface drainage for all lots;
(7) Describe all storm drainage systems including the completion date of any structures required to be constructed, and identify the entity that is responsible for construction; and
(8) Illustrate or describe all subsequent irrigation water conveyances to each parcel if irrigated within the last 5 years.
(H) Reference material.
(1) Critical Area Treatment for Urban Development, Cuidad SWCD; USDA, SCS; Albuquerque Health & Energy Dept. Air Pollution Control Division.
(2) Guide for Interpreting Engineering Uses of Soils, USDA, SCS.
(3) Engineering Field manual for Conservation Practices, Chapter 2; Peak Rates of Discharge for Small Watersheds in New Mexico, USDA, SCS.
(4) Field Office Engineering Field Handbook, USDA, SCS.
(5) Field Office Technical Guides, USDA, NRCS.
(6) Field Office Technical Notes, USDA, NRCS.
(7) Natural Resource Conservation District Practice Standards for Terrain Management, NM Association of Soil and Water Conservation Districts New Mexico Subdivision Review Guide, USDA, SCS; 1989.
(8) National Agronomy Manual, USDA, SCS.
(9) National Plant Materials Handbook, USDA, SCS.
(10) National Range Handbook, USDA, SCS.
(11) National Soils Handbook, USDA, SCS.
(12) Published Soil Surveys and Soils Interpretation Sheets by the USDA, NRCS TR 20; Computer Program or Project Formulation; Hydrology, USDA, SCS.
(13) TR 55; Urban Hydrology for Small Watersheds, USDA, SCS.
(14) National Catalog of Erosion and Sediment Control and Storm Water Management; Guidelines for Community Assistance, NRCS August 1995.
(I) Supporting data requirements terrain management plan development standards.
(1) In instances of phased development the local district shall require those portions of the terrain management plan for the entire proposed development that it deems necessary to allow for the conducting of adequate phase development reviews.
(2) A critical factor impacting terrain management, especially in those cases where the developer is selling undeveloped lots is what is allowed to happen after the sale. Normal sound development practices in these situations include a set of restrictive covenants or homeowner association by-laws. These documents set forth many do's and don'ts that will be allowed in the subdivision. Since these can have a profound impact on the overall plan for terrain management, the Valencia Soil and Water Conservation District shall require that these be made available at the time of the initial review of any subdivision packet received for review.
(J) Soils.
(1) Soils having severe limitations, or which are shown unsuitable, for the intended purposes should not be used for the purpose unless the developer has clearly shown in the terrain management plan how these limitations will be overcome.
(2) Below are the major categories of land use to be used in reviewing the terrain management plan of subdivision. Information about any of these categories which are pertinent to the development proposal should be included in the terrain management plan.
(a) Building site development.
(b) Construction materials.
(c) Local roads and streets.
(d) Underground utilities.
(e) Water control structures.
(f) Erosion control structures.
(g) Playgrounds.
(h) Paths and trails.
(i) Sewage disposal.
(j) Irrigation easements.
(K) Grading.
(1) Land grading, filling and clearing operations can cause many problems when performed incorrectly, such as when leaving large areas open to wind or water erosion.
(2) In addition to conforming to soil suitability, grading, filling and clearing operations, including road development, shall be designed to fulfill the following requirements and be included in the terrain management plan as outlined below.
(a) Preserve, match or blend with the natural contours of the land. The plan should adequately describe how grading operations will be performed to blend slopes and fills into the natural contours of the land.
(b) The plan should indicate whether the subdivider intends to retain or replace trees and other native vegetation, to stabilize hillsides and cut/fill slopes, retain moisture, reduce erosion, reduce runoff, and preserve the natural scenic beauty.
(c) Cuts and fills should prevent the deposit of sediment into floodplains, drainage channels, watercourses, and water bodies.
(3) The following discharges attributable to grading are prohibited whether the discharge is direct or indirect:
(a) Sediment and other organic or earthen materials discharged into a water course, water body, drainage channel or floodplain; and
(b) Material placed in any position, which would make it susceptible to erosion and deposition into a watercourse, water body, drainage channel or floodplain.
(4) The plan for grading, land forming, and protective cover should provide for the prevention of soil sedimentation.
(5) The plan should call for temporary or permanent structural measures to prevent damaging runoff waters from originating on the slope itself, if applicable.
(6) Planned structural measures should adequately provide for the limitations of the site.
(7) Whenever the native ground cover is removed or disturbed, or whenever fill material is placed on site, the plan should provide for the exposed surface to be treated to the extent necessary to prevent dust from blowing off the construction site.
(8) The work schedule for the grading and filling operations should limit the time soil is exposed to the shortest possible period before cover is established.
(9) Provisions should be made for disposal of vegetation during the clearing operation. The plan should describe the disposition of earth removed during grading operations.
(10) The maximum cut and fill slopes should be compatible with soil stability or readability as shown on the soil survey and/or county regulations.
(11) The plan should include provisions to prevent runoff from flowing over the face of the slope. If mechanical stabilization measures are planned for slope containment:
(a) These structures should blend with the landscape.
(b) If structures do not blend in, landscape screening should be planned.
(c) If a borrow area is shown, revegetation should be planned for the disturbed area.
(d) If arroyos or other overflow areas are in the planning area, plans should include rundowns to a safe outlet. Plans should include provisions for water and erosion control in borrow ditches along streets and roads.
(12) A clear statement of whom will be responsible for maintenance of all drainage and erosion control structures.
(L) Floodplain management.
(1) Flood line elevations are locations are of primary importance. It is imperative that the 100-year flood line elevations and locations be shown on the plat map. Damage from flooding is a function of flow depths and velocity. In appraising the flood damage potential the magnitude and location of the velocities should be considered. Erosion and sediment deposition are good indicators of damage that has occurred in the past.
(2) Even the smallest of watersheds has a floodplain, but the intent of the review is to note those drainage courses that will flood and impact the proposed land use of the subdivision. Areas of potential flooding are identified in the soil limitations of any USDA prepared soil survey. While these are not usually accurate enough to identify the 100 year flood zone, they will be useful indicators of areas needing careful study by the developer. The use of FEMA flood hazard maps by themselves are also not considered adequate for locating all possible 100 year floodplains within the development. These maps commonly depict the larger drainage flood hazard areas, but do not delineate the smaller areas, which need to be identified within a proposed subdivision.
(3) The smaller drainage courses must not be overlooked. They must be properly identified as potential floodplain hazards if these drainage courses cross numerous lots where activities by the upstream lot owner may directly or indirectly change or alter the flow pattern of these watercourses. The developer may note the major watercourses having floodplains on the plat maps, and additionally must also identify those smaller drainage channels and watercourses which cross a number of lots and present a potential hazard if altered by upstream activities. A perpetual easement for facilitating the natural drainage patterns of smaller watercourses should be encouraged and may be required where deemed necessary. This will allow floodwaters to move through the natural as well as the manmade flood channels without being obstructed. Care must be given to consider those water courses that do not have definite and distinct banks but are floodplains due to an overland flow condition.
(M) Storm drainage plan.
(1) Subdivisions and developments shall be planned, constructed and maintained to:
(a) Protect and preserve existing natural drainage channels except where erosion and water control measures are found necessary and approved by the local district;
(b) Provide temporary measures to prevent damaging runoff waters from leaving the site until construction is completed and permanent control measures are installed;
(c) Protect structures and other works from flood hazards using the 100-year frequency storm for calculating flood levels;
(d) Provide a system where in runoff water within the subdivision is removed without causing harm or damage to the environment, property, or persons, inside or outside the subdivision area;
(e) Assure that water drained from the subdivision does not contain pollutants or sedimentary materials of any greater quantity than would occur in the absence of the subdivision; and
(f) Assure that waters are drained from the subdivision in a manner that they will not cause erosion outside the subdivision to any greater extent than would occur in the absence of the subdivision.
(2) Road construction shall ensure proper drainage conditions. Roads shall be designated to:
(a) Water ponding areas as a result of road construction should be avoided unless plans are developed that will adequately address the conditions;
(b) Roads planned to be used in collecting or disposing of runoff shall be designed to insure adequate control of the flows that will prevent erosion and sedimentation;
(c) Road drain outlets into an existing drainage course or into a controlled outlet shall be designed to outlet into controlled area and prevent erosion on the drainage course and runoff area;
(d) Provide road culverts which are properly sized and located and of adequate length; and
(e) Provide adequate protection for road culvert inlets and outlets.
(3) All storm drainage systems shall be constructed in accordance with the standards of the Valencia Soil and Water Conservation District as deemed necessary for the site conditions of that proposed subdivision. If the drainage basin wherein the subdivision is located is only partially developed, the Valencia SWCD shall require that the design and the construction of the drainage system have sufficient flow capabilities to adequately serve the entire drainage basin. This is based on the assumption the entire basin will be developed.
(4) Development of an area is almost certain to cause an increase in runoff and sediment. The possible adverse effects of the increase should be analyzed. Special consideration should be given to the existing or planned bridge, culvert, and road crossing sizes and the stability and capacity of the existing or planned watercourses. All planned construction of roads and their appurtenances shall be reviewed to ensure they do not adversely impact the storm drainage flows. It is recognized that stable watercourses may start to degrade when exposed to larger, more frequent or longer flows that may result from development.
(5) Diversions, debris basins, retaining walls, terraces, berms and vegetative means should be used as needed to reduce the sediment and runoff. It is recognized that after an area is treated and sediment levels of storm runoff are reduced, the water is once again more likely to be able to increase erosion in areas that previously impacted due to its new found ability to erode and transport sediment.
(6) Regarding and shaping of large natural channels usually increases the channel velocity, which results in increased erosion unless measures are taken to slow velocities and protect the banks.
(7) Excavated and filled slopes should be generally be 3 to 1 or flatter.
(N) Erosion control.
(1) The plan should clearly indicate that installed measures will prevent or control erosion.
(2) As a minimum the following items should be considered:
(a) Road grades should be designed flat enough to prevent erosion, based on the soils involved;
(b) Borrow areas or drainage features should be designed to prevent erosion or sediment deposition; and
(c) Culvert inlets and outlets should be properly protected from erosion and sedimentation.
(3) Plans should indicate where critical area treatment or special plantings will be needed. If so, the plans should be in keeping with the landscaping and revegetation plan procedures.
(4) Plans should indicate where temporary soil stabilization will be needed during development. If so, it should be adequately planned in accordance with the Valencia SWCD/Natural Resources Conservation Service Field Office Technical Guides.
(5) Soil stabilization measures should be planned to protect permanent slopes where land forming activities have taken place.
(O) Landscaping and revegetation.
(1) Revegetation is an important part of any subdivision plan. A definite time schedule for installing plant cover is necessary to prevent erosion. The need for revegetation is an integral part of several other sections involved in terrain management.
(2) The following items will be considered when reviewing the vegetation portion of the subdivision plan:
(a) 1. Species scheduled for planting should be adapted to the soils and the local climate;
2. Any species considered to be noxious, or a weed species that could enhance the distribution of undesirable species will not be allowed;
(b) Planting dates shown in the plan should agree with the Valencia SWCD and NRCS Field Office Technical Guides;
(c) Seeding rates shown in the plan should meet the minimum set forth in the Valencia SWCD and NRCS Field Office Technical Guides;
(d) Seeding or planting methods should be compatible with the methods in the Field Office Technical Guides;
(e) Mulching of seeded area should be included as part of the plan. Mulching plans should be compatible with the Field Office Technical Guides and the Critical Area Treatment for Urban Development publication; and
(f) Existing vegetation should be left undisturbed whenever possible. The plan should ensure that remaining vegetation is not adversely impacted during construction of the subdivision.
(Ord. passed 5-1-2000) Penalty, see § 151.999